Network load test equipment

I'm looking for equipment that can be used to load test network equipment such as switches, routers, firewall, and load balancers with pre-defined traffic patterns at differing rates. Ideally, this is only something I think I'll need 2-3x a year, so purchasing is not necessarily justifiable. I'd prefer to rent. What products have you used? Where did you get them from? I need to be able to run pre-defined traffic patterns at various rates, in excess of 10Gbps in most cases. Thanks! Greg